This invention is concerned with liquid acid catalysts for hydrocarbon reactions and a method for reacting hydrocarbons employing such catalyst.
In the past hydrocarbon conversion reactions such as alkylations, acylations, rearrangements, and isomerizations have been carried out in the presence of strong Lewis acids or strong Bronsted acids. A Lewis acid is a compound in which the normal electronic grouping about the central atom can accept an electron pair from a Lewis base which is any compound capable of donating an electron pair. Such Lewis acids include fluorides, chlorides, and bromides of aluminum, zinc, titanium, zirconium, antimony and iron. Bronsted acidity, on the other hand, reflects the ability of a protonic acid to transfer a proton to a base. Bronsted acids suitable as-catalysts for hydrocarbon conversion reactions include strong protonic acids such as liquid sulfuric acid, hydrogen fluoride, phosphoric acid and trifluoromethanesulfonic acid. Generally these protonic acids have an H.sub.o value on the Hammett scale of -11 or less, and they have been applied in organic syntheses for a variety of reactions, including the alkylation of arenes with alkenes, alcohols, and esters; transalkylation of arenes with polyalkylbenzenes; acylation, sulfonation, and nitration of aromatic compounds; acylation of alkenes; and hydration of lower olefins. Common to all these acid-catalyzed reactions is the formation of carbocations as intermediates.
The effectiveness of such Lewis acid and Bronsted acid catalysts for hydrocarbon conversions is directly related to the acidity of the catalyst material toward the hydrocarbon substrate. Any modification which increases the acidity of the acid will result in an increase of its catalytic activity.
It has now been found that the acidity of a strong liquid Bronsted acid can be enhanced by adding to it an ion-stabilizing agent to form a liquid catalyst with increased catalytic activity.